1. Field of the Invention
The present invention relates to a method for mounting coils to the inner periphery of a cylindrical article and an apparatus for practicing the method. More particularly, the present invention relates to a coil mounting method suitable for mounting coils to coil grooves formed in the inner periphery of a cylindrical core in assembling, for example, a cylindrical rotary transformer used in the cylinder of a video tape recorder (VTR), as well as an apparatus for practicing the method.
2. Description of the Prior Art
Recently there has been a tendency to reduce the size and increase the function of video tape recorders (VTR). To cope with this tendency, studies have been made to use a cylindrical rotary transformer in place of the conventional plate shape in VTR.
The coils in the core of such transformers must be received completely in coil grooves formed in the inner peripheral surface of the core so as not to project inwardly from the same surface. This operation can be done only manually over a long time, thus impeding efficient production.
In an effort to overcome this problem there has been proposed such a technique as disclosed in Japanese Patent Laid Open No. 54411/87 (U.S. Pat. No. 4,724,604)as a method for automatically mounting coils to coil grooves formed in the inner periphery of a cylindrical core.
According to the proposed technique, one or several portions of a coil are deformed on the inner peripheral side by means of a coil deforming shaft having a plurality of gripping fingers so that a circumscribed circle or diameter of the coil is contracted; the thus-deformed coil is inserted into a core having coil grooves formed in the inner periphery thereof; and then the deformed portions of the coil thus inserted into the core are expanded by means of a coil expanding shaft having expanding fingers so that the undeformed portions of the coil are fitted into a coil groove of the core. Thereafter, the entire periphery of the coil is pushed against the bottom of the coil groove by means of a pressing roller. In this way there is obtained a product having coils along its inner periphery.
In the above conventional technique, however, the coil is pre-formed in conformity with the diameter of an annular groove which is larger than the diameter of the inner periphery of the core, and is inserted against the inner peripheral surface of the core under utilization of the elasticity of the coil and fitted into a coil groove, the following problems occur.
First it is necessary to use a number of jigs, including a jig for forming a coil in conformity with a predetermined diameter, a jig for holding the coil on the forming jig from the outside, a jig for deforming the thus-held coil inwards and inserting it into a core, a jig for expanding the inserted coil, and a jig for pushing the coil against a coil groove of the core. Thus, not only are many jigs needed, but also a large number of steps must be followed.
Moreover, there is a concern that the coil will be deformed when the coil is pushed against a core groove of the core by means of a roller or the like after its expansion in the core. Particularly, since the coil is deformed to reduce the diameter of its circumscribed circle before it is inserted into the core, the thus-deformed portions will not be restored to the original state completely, thus giving rise to a likelihood of deflection.
Further, since the coil is pre-formed in conformity with the coil grooves of the core, it is necessary to separate the coil into deformed and undeformed portions and enlarge the deformation of the deformed portions when inserting the coil into the core. Besides, the jig for this operation becomes complicated in structure.